(a) Field of the Invention
The present invention relates to a III-V compound semiconductor device having a conductive layer consisting of a nitride of a high-melting transition metal.
(b) Description of the Prior Art
ICs using a III-V compound semiconductor, especially GaAs, have recently undergone considerable development. The ion implantation technique is indispensable in the manufacturing process of these ICs. In association with the ion implantation technique, requirements for materials for an electrode wiring metal layer, an insulating film and so on become strict in a different sense as compared with those for Si ICs.
For example, in order to manufacture a GaAs semiconductor device, Si ions are selectively ion-implanted in a desired portion of the surface of a GaAs substrate at a predetermined dose, and the resultant structure must be annealed at a temperature of 800.degree. to 850.degree. C. for 15 to 20 minutes so as to activate the doped ions. In this selective ion implantation, an SiO.sub.2 pattern, an Si.sub.3 N.sub.4 pattern or a photoresist pattern is used as a mask. However, occasionally, a metal layer is deliberately used as a mask, and the metal layer is left after ion implantation to serve as an electrode.
The self alignment technique in the manufacture of a GaAs MOSFET IC which has recently received a great deal of attention is a typical example. This technique is the most promising technique since an insulating film, which provides good characteristics at an interface between the insulating material and the semiconductor in the Si semiconductor device, is not currently available.
A high-melting transition metal such as W, TiW (10% of Ti) and Ta can be used as a metal mask material which can be used with the self alignment technique. In particular, TiW is preferred because of its good resistance to high temperatures. However, in general, when a high-melting transition metal or its alloy is heated at a temperature of 700.degree. C. or higher, it quickly reacts with the GaAs of the GaAs substrate to change electrical characteristics such as a change in the height .phi.n of a Schottky barrier and an increase in an n value as an index value of a rectification property of the barrier. As a result, the required characteristics cannot be obtained.
In order to eliminate these drawbacks, TiW and Mo silicides have received a great deal of attention. It is known that a silicide is an intermetallic compound of a metal and silicon. In general, a high-melting transition metal silicide has a very low resistivity of not more than about 10.sup.-4 .OMEGA..multidot.cm, a melting point of not higher than about 2,000.degree. C., and a strong bonding force between the atoms. In this manner, the high-melting transition metal silicide is known as a thermally stable material and has been used as a material for various electrode and wiring layers.
A silicide is sputtered onto the GaAs semiconductor substrate. A target of a desired silicide or a target of a desired metal and Si is used. In the former case, a silicide target having the desired composition must be prepared in advance. In the latter case, it is very difficult to obtain a desired composition.